910 STERNUM 
saving that the partition is traversed by the TRACHEA and ESOPHAGUS. 
The spina sternalis is not, as often stated, the homologue of the 
manubrium sterni of Mammals, for that is equivalent to the right and 
left anterior lateral processes.' It is to be understood that so far 
all these structures are cartilaginous. 
Ossification of the Sternum does not begin till after it has 
attained its final shape, and proceeds from various centres, which, 
notwithstanding the elaborate studies of Geoffroy St.-Hilaire, 
L’Herminier and Parker cannot always be recognized in the different 
groups of Birds, chiefly owing to the variable situation of these 
centres—one or another being suppressed and its place taken by 
the extension of its neighbours. As a rule ossification begins 
earliest where the greatest strength or resistance is needed. Thus 
in Rhea, Galline, Turnix, Lestris and the Passeres, each anterior 
lateral process has its pro-osteon (Parker), but in many other forms, 
as Ardea, Rallide and Ibis, these processes possess no special centre 
of ossification, and are converted into bone by the extension of the 
plewrostea, which last occur in the majority of Birds, though absent 
in Turnia and the Gallinx, and lie in the lateral margin of the 
Sternum, where the ribs are attached: coracostea occur sometimes 
at the anterior end of the Sternum, near the articulation of the 
Coracoids, and in some Birds metostea are the centres whence the 
posterior lateral processes ossify, while the lophosteon (Parker), which 
may be single, multiple or paired, is the centre of ossification for 
the keel. 
The Duck and the common Fowl may be cited in particular 
illustration of this variability. In the former no trace of ossifica- 
tion is visible before the bird is about 6 weeks old, when the 
centres appear in the anterior lateral processes. By the end of 
the 7th week ossification extends over the lateral rib-bearing 
margin. A few days later it reaches the coracoidal portion, and in 
the course of the following weeks numerous irregular patches of 
1 The synonymy of the various parts of the Avine Sternum being somewhat 
perplexing, the following may be of some use :— 
Processus lateralis anterior=proc. costalis of various authors ; prosternal latéral, 
L’Herminier ; proc. sterno-coracoideus or precos- 
talis, Fiirbringer. 
posterior=lateral xiphisternal process, Parker ; trabecula intcr- 
media and trab. lateralis, Fiirbringer. 
93 obliquus=trab. lateralis, Fiirbringer. 
Metasternum=iphosternwm of various authors; median xiphisternal process, 
” 29 
Parker. 
Spina sternalis=rostrwm, wrongly called manubriwm by many ; episternum, 
Owen. 
externa=manubrium, rostrum, episternal process, apophyse sous- 
épisternale or supériewre, inferior rostrum. 
interna =apophyse sousépisternale, superior rostrum. 
9 29 
37 39 
